1. Field of the Invention
The present invention relates to a tool and a method for the fabrication thereof for forming bores of unusual or asymmetrical cross section in the propellant in solid rocket motors.
2. Description of the Prior Art
Solid propellant rocket motors utilize a thin-wall cylindrical rocket motor case that is closed at the forward end and has a nozzle at the other end for the emission of exhaust gases from the case. A case-bonded solid propellant may be cast into the rocket motor case after a core of fixed and desired configuration, generally made of metal, has been placed in the case with the propellant filling the space between the core and the case, after which the propellant grain is cured. The core is then removed leaving a cavity or bore having a constant or unchanging cross section the shape of which corresponds to the constant cross section of the core, thus duplicating the exterior contour of the core.
The core may possess a plurality of star points that are arranged symmetrically with relation to the longitudinal axis of the core, the number of star points varying according to the individual requirement of the particular solid propellant rocket motor that is involved.
Solid propellant rocket motor cores may also possess unusual or asymmetric geometries such as, but not limited to, a "hook" as disclosed, for example, in U.S. Pat. No. 3,529,550 to Ralph W. Snowden, issued on Sept. 22, 1970 and assigned to the assignee of the present invention. Such cores enable many variations in the characteristics of the solid propellant grain such as are needed to meet specific requirements of a solid propellant rocket motor and such as occur when the number of star points of a symmetrical core is varied. Cores of such unusual configuration have advantages including high loading density and reduction of strains in the solid propellant grain that are encountered by the solid propellant rocket motor under temperature changes that occur during its operational requirements.
The fabrication, however, of metal cores in accordance with the practice of the prior art to form unusual or asymmetrical constant cross section bores for use in solid rocket motors requires complex, and hence, expensive machining. The "hook" configuration is complicated and, in general, can be made only with the use of three-dimensional numerical control (NC) controlled machining capability.
Thus, there is a need and a demand for improvement in the tools and the method of the fabrication thereof for forming such tools quickly with little requirement for special machining capability. The present invention was devised to fill the technological gap that has existed in the art in this respect.